The present invention relates to (1) an optical muzzle blast detection and counterfire targeting system for remotely detecting the location of muzzle blasts produced by rifles, artillery and other weapons and similar explosive events, especially sniper fire; and (2) a system for directing counterfire weapons on to this location.
Hillis U.S. Pat. No. 5,686,889 relates to an infrared sniper detection enhancement system. According to this Hillis patent, firing of small arms results in a muzzle flash that produces a distinctive signature which is used in automated or machine-aided detection with an IR (infrared) imager. The muzzle flash is intense and abrupt in the 3 to 5 mum band. A sniper detection system operating in the 3 to 5 mum region must deal with the potential problem of false alarms from solar clutter. Hillis reduces the false alarm rate of an IR based muzzle flash or bullet tracking system (during day time) by adding a visible light (standard video) camera. The IR and visible light video are processed using temporal and/or spatial filtering to detect intense, brief signals like those from a muzzle flash. The standard video camera helps detect (and then discount) potential sources of false alarm caused by solar clutter. If a flash is detected in both the IR and the visible spectrum at the same time, then the flash is mostly probably the result of solar clutter from a moving object. According to Hillis, if a flash is detected only in the IR, then it is most probably a true weapon firing event.
In Hirshberg U.S. Pat. No. 3,936,822 a round detecting method and apparatus are disclosed for automatically detecting the firing of weapons, such as small arms, or the like. According to this Hirshberg patent, radiant and acoustic energy produced upon occurrence of the firing of a weapon and emanating from the muzzle thereof are detected at known, substantially fixed, distances therefrom. Directionally sensitive radiant and acoustic energy transducer means directed toward the muzzle to receive the radiation and acoustic pressure waves therefrom may be located adjacent each other for convenience. In any case, the distances from the transducers to the muzzle, and the different propagation velocities of the radiant and acoustic waves are known. The detected radiant (e.g. infrared) and acoustic signals are used to generate pulses, with the infrared initiated pulse being delayed and/or extended so as to at least partially coincide with the acoustic initiated pulse; the extension or delay time being made substantially equal to the difference in transit times of the radiant and acoustic signals in traveling between the weapon muzzle and the transducers. The simultaneous occurrence of the generated pulses is detected to provide an indication of the firing of the weapon. With this arrangement extraneously occurring radiant and acoustic signals detected by the transducers will not function to produce an output from the apparatus unless the sequence is corrected and the timing thereof fortuitously matches the above-mentioned differences in signal transit times. If desired, the round detection information may be combined with target miss-distance information for further processing and/or recording.
According to the present invention, an infrared camera stares at its field of view and generates a video signal proportional to the intensity of light. The camera is sensitive in the infrared spectral band where the intensity signature of the flash to be detected minus atmospheric attenuation is maximized. The video signal is transmitted to an image processor where temporal and spatial filtering via digital signal processing to detect the signature of a flash and determine the flash location within the camera""s field of view. The image processing circuits are analog and digital electronic elements. In another aspect and feature of the invention, the image processing circuits are coupled to target location computation circuits and flash location information is transmitted to the targeting location computation circuits. The targeting computation circuit is digital electronic circuitry with connections to the other devices in the system. The field of view of the camera is correlated to the line of sight of the confirmation sensor by using aim point measurement devices which are coupled to the target computation processor. The displays are video displays and show camera derived imagery superimposed with detection and aiming symbology and system status reports. The user interface devices are keypads and audible or vibrational alarms which control the operation of the system and alert the user to flash detections which are equated to sniper firing, for example. In still another aspect of the invention, the weapon aim point measurement devices include inertial measurement units, gyroscopes, angular rate sensors, magnetometer-inclinometers, or gimbaled shaft encoders. Visual target confirmation sensors are binoculars or rifle scopes with associated aim point measurement devices. Counterfire weapons contemplate rifles, machine guns, mortars, artillery, missiles, bombs, and rockets.
The basic objective of the present invention is to provide an improved muzzle blast detector system and method which uses multi-mode filtering to eliminate and/or minimize false alarms.
Another object of the invention is to provide a muzzle blast detector which accurately locates direction and range to muzzle blast source.
Another object of the invention is to provide a sniper detection method and apparatus which uses temporal, spectral and spectral filtering to discriminate between actual muzzle blasts and non-muzzle blast infrared generating events.